This invention relates to serial printers which use a formed character print element (e.g., rotatable print wheel) and more particularly to an improved electronic control system thereof which yields greater mechanical reliability, lower energy usage, lower vibration and acoustic noise, and faster printing.
Serial formed character printers generally use a print wheel (such as a so-called "daisy wheel") mounted on a carriage. The carriage is mounted for linear movement along a line to be printed. The print wheel is mounted for rotation to enable different characters to move sequentially past a print hammer. In typical operation, a carriage motor is controlled to step the carriage in an incremental fashion, stopping at each character position to be printed. A print wheel motor is controlled to rotate the print wheel concurrently with the carriage movement to position a selected character adjacent the hammer. When both the carriage and print wheel come to rest at their desired destination positions, the hammer is fired to print the character. The carriage and print wheel can then be repositioned to print the next character.
The carriage and print wheel motors may be operated open loop if stepper motors are used but more typically, for higher speed operation, servo motors are employed and separate carriage and print wheel servo loops are utilized.
It has been recognized that the repeated starting and stopping of the carriage (which typically weighs about two pounds) using the maximum practical acceleration and deceleration produces high mechanical stresses and wear which can cause reliability problems in high speed printers. Moreover, the necessity to accelerate from rest to some maximum velocity, and then to decelerate back to rest, limits the speed at which the printer can operate.
In view of the foregoing, the present invention is directed to an improved printer control system capable of adaptively controlling the carriage speed during each carriage positioning interval to thereby permit printing without stopping the carriage, i.e., "on the fly."